SET009 · Sets, relations & logic · Classes 9–11
Set difference
The difference A − B contains the elements of A that are not in B: the part of circle A outside B.
A − BSet difference
📐 Formula
A − B = {x : x ∈ A and x ∉ B}
✏️ Worked example
Multiples of 2 minus multiples of 3 (up to 12) = {2, 4, 8, 10}.
🌍 Where it is used
Students in the choir but not in the band.
❓ Quick check
{1, 2, 3, 4} − {2, 4} = ?
🏋️ Practice
Easy{a, b, c} − {b} = ?
Answer: {a, c}
MediumIs A − B the same as B − A?
Answer: No, in general
ChallengeA − A = ?
Answer: ∅